Surfactants are the single most important cleaning ingredient in household and personal care cleaning products. Environmental regulations, consumer habits, and consumer practices have forced new developments in the surfactant industry to produce lower-cost, higher-performing, and environmentally friendly products. Examples of developments in the surfactant industry are described by J. Scheibel in the Journal of Surfactants and Detergents, “The Evolution of Anionic Surfactant Technology to Meet the Requirements of the Laundry Detergent Industry,” volume 7, number 4, October, 2004 (“Scheibel JSD Article” hereinafter), which is incorporated herein by reference. Today, challenges facing the surfactant industry include colder wash temperatures, less efficient builders, liquid products without calcium control, and a push for reduced surfactant use overall because of the perceived environmental impact of surfactants.
Alkylbenzene sulfonates (ABS) are surfactants derived from tetrapropylene that have very complex branching structures (e.g., 3 or 4 branches per molecule). The structure below illustrates one example of a hard ABS molecule, which has branching near the polar head group and in the middle of the surfactant.

ABS surfactants were prominent until the early 1960s when they were subjected to environmental regulations for being poorly biodegradable. ABS surfactants were then replaced with the readily biodegradable linear alkylbenzene sulfonate (LAS) surfactants, which are easily obtainable and currently in use today. Use of LAS surfactants and other similar linear surfactants is limited because they have poor solubility in cold- and hard-water conditions. In fact, more than half of the LAS detergent in products may be lost during use due to the formation of multilayered vesicles that resemble large onion-like structures. Formulators can increase the solubility of linear surfactants by, for example, introducing co-surfactants or by using linear alcohol ethoxylated sulfates (AES). However, AES surfactants have lower surface activity as well as lower mass efficiency than LAS surfactants. Further, the use of co-surfactants or AES surfactants limits formulation flexibility and can add substantial cost to the detergent. ABS, LAS, and AES surfactants are described in detail in the Scheibel JSD article.
Surfactants with light, mid-chain branching, such as highly soluble alcohol sulfate (HSAS) surfactants derived from petroleum feedstocks, were then developed for use in consumer products. HSAS surfactants, which are illustrated in the Scheibel JSD article, as well as U.S. Pat. Nos. 6,020,303; 6,060,443; and 6,335,312; and U.S. Patent Application Publication No. 2010/0137649 (each incorporated herein by reference), traditionally contain alkyl branching on carbon atoms that are at both the even and odd-numbered positions of the longest linear chain of the surfactant. HSAS surfactants provide good cleaning ability in cold, hard water, have high solubility, good grease removal properties, and good biodegradability. Because surfactants with mid-chain branching are widely used by consumers, a need exists to further improve their biodegradability.